Method and system for authenticating an accessory

ABSTRACT

A method, system, and connector interface for authenticating an accessory. the method includes performing a first authentication operation on the accessory by the media player, where an authentication certificate is validated; and performing a second authentication operation on the accessory by the media player, where an authentication signature is validated. According to the system and method disclosed herein, the media player and accessory may utilize a plurality of commands utilized in a variety of environments such as within a connector interface system environment to control access to the media player.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/347,511, filed on Jan. 10, 2010, now U.S. Pat. No. 8,590,036, which is a continuation of U.S. patent application Ser. No. 11/476,999, filed on Jun. 27, 2006, now U.S. Pat. No. 8,117,651, which are incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to electrical devices and more particularly to electronic devices such as media players that communicate with accessory devices.

BACKGROUND OF THE INVENTION

A media player stores media assets, such as audio tracks or photos that can be played or displayed on the media player. One example of a media player is the iPod® media player, which is available from Apple Inc. of Cupertino, Calif. Often, a media player acquires its media assets from a host computer that serves to enable a user to manage media assets. As an example, the host computer can execute a media management application to manage media assets. One example of a media management application is iTunes®, version 6.0, produced by Apple Inc.

A media player typically includes one or more connectors or ports that can be used to interface to the media player. For example, the connector or port can enable the media player to couple to a host computer, be inserted into a docking system, or receive an accessory device. There are today many different types of accessory devices that can interconnect to the media player. For example, a remote control can be connected to the connector or port to allow the user to remotely control the media player. As another example, an automobile can include a connector and the media player can be inserted onto the connector such that an automobile media system can interact with the media player, thereby allowing the media content on the media player to be played within the automobile.

Numerous third-parties have developed accessories for use with media players. An accessory may be used with the media player as long as a compatible connector or port is utilized. Accessories interact with the media player using an accessory protocol. One example of an accessory protocol is referred to as iPod Accessory Protocol (iAP), which is available from Apple, Inc. of Cupertino, Calif. The accessory protocol includes commands which have been typically been made freely accessible to accessory developers. A problem with the commands being freely accessible is that they can be used by unauthorized or counterfeit accessory devices.

One solution is to perform authentication operations on an accessory device. Accordingly, the accessory devices would not have any access to the media player until after the authentication process is complete.

Thus, there is a need for improved techniques to control the nature and extent to which accessory devices can be utilized with other electronic devices.

BRIEF SUMMARY OF THE INVENTION

A method, system, and connector interface for authenticating an accessory are disclosed. The method includes performing a first authentication operation on the accessory by the media player, where an authentication certificate is validated; and performing a second authentication operation on the accessory by the media player, where an authentication signature is validated.

According to the system and method disclosed herein, the media player and accessory may utilize a plurality of commands in a variety of environments such as within a connector interface system environment to control access to the media player.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a docking connector in accordance with the present invention.

FIG. 2A is a front and top view of a remote connector in accordance with the present invention.

FIG. 2B illustrates a plug to be utilized in the remote connector.

FIG. 2C illustrates the plug inserted into the remote connector.

FIG. 3A illustrates the connector pin designations for the docking connector.

FIG. 3B illustrates the connection pill designations for the remote connector.

FIG. 4A illustrates a typical FireWire connector interface for the docking connector.

FIG. 4B illustrates a reference schematic diagram for an accessory power source.

FIG. 4C illustrates a reference schematic diagram for a system for detecting and identifying accessories for the docking connector.

FIG. 4D is a reference schematic of an electret microphone that may be connected to the remote connector.

FIG. 5A illustrates a media player coupled to different accessories.

FIG. 5B illustrates the media player coupled to a computer.

FIG. 5C illustrates the media player coupled to a car or home stereo system.

FIG. 5D illustrates the media player coupled to a dongle that communicates wirelessly with other accessories.

FIG. 5E illustrates the media player coupled to a speaker system.

FIG. 6 is a flow chart, which illustrates a process for controlling access to a media player.

FIG. 7 is a flow chart, which illustrates a process for authenticating an accessory.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to electrical devices and more particularly to electrical devices such as media players that communicate with accessory devices. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.

A method and system in accordance with the present invention are provided for authenticating an accessory. The method includes performing a first (background) authentication operation on the accessory by the media player, wherein an authentication certificate is validated. In one embodiment, the authentication operations are handled in the background such that the media player is operative to process commands after authentication has begun but before the authentication has completed. This allows the media player and the accessory to interact immediately rather than waiting until after the authentication process has completed successfully. The method also includes performing a second authentication operation on the accessory by the media player, wherein an authentication signature is validated. In one embodiment, the media player verifies the authentication signature using a public key provided in the certificate. The media player and accessory may utilize a plurality of commands in a variety of environments to facilitate controlling access to the media player. One such environment is within a connector interface system environment such as described in detail herein below.

Although the authentication of an accessory is described herein below, one of ordinary skill in the art recognizes that the procedures described below may be applied to the authentication of the media player and such application would be within the spirit and scope of the present invention.

Connector Interface System Overview

To describe the features of the connector interface system in accordance with the present invention in more detail, refer now to the following description in conjunction with the accompanying drawings.

Docking Connector

FIGS. 1A and 1B illustrate a docking connector 100 in accordance with the present invention. Referring first to FIG. 1A, the keying features 102 are of a custom length 104. In addition, a specific key arrangement is used where one set of keys is separated by one length at the bottom of the connector and another set of keys is separated by another length at the top of the connector. The use of this key arrangement prevents noncompliant connectors from being plugged in and causing potential damage to the device. The connector for power utilizes a Firewire specification for power. The connector includes a first make/last break contact to implement this scheme. FIG. 1B illustrates the first make/last break contact 202 and also illustrates a ground pin and a power pin related to providing an appropriate first make/last break contact. In this example, the ground pin 204 is longer than the power pin 206. Therefore, the ground pin 204 would contact its mating pin in the docking accessory before the power pin 206, minimizing internal electrical damage of the electronics of the device.

In addition, a connector interface system in accordance with the present invention uses universal serial bus (USB), universal asynchronous receiver-transmitter (UART), and Firewire interfaces as part of the same docking connector alignment, thereby making the design more compatible with different types of interfaces, as will be discussed in detail hereinafter. In so doing, more remote accessories can interface with the media player.

Remote Connector

The connection interface system also includes a remote connector which provides for the ability to output and input audio, provides I/O serial protocol, and provides an output for video. FIG. 2A is a front and top view of a remote connector 200 in accordance with the present invention. As is seen, the remote connector 200 includes a top headphone receptacle 202, as well as a second receptacle 204 for remote devices. FIG. 2B illustrates a plug 300 to be utilized in the remote connector. The plug 300 allows the functions to be provided via the remote connector. FIG. 2C illustrates the plug 300 inserted into the remote connector 200. Heretofore, all of these features have not been implemented in a remote connector. Therefore, a standard headphone cable can be plugged in, but also special remote control cables, microphone cables, and video cables could be utilized with the remote connector.

To describe the features of the connector interface system in more detail, please find below a functional description of the docking connector, remote connector and a command set in accordance with the present invention.

Docking and Remote Connector Specifications

For an example of the connector pin designations for both the docking connector and for the remote connector for a media player such as an iPod® device by Apple, Inc., refer now to FIGS. 3A and 3B. FIG. 3A illustrates the connector pin designations for the docking connector. FIG. 3B illustrates the connection pin designations for the remote connector.

Docking Connector Specifications

FIG. 4A illustrates a typical Firewire connector interface for the docking connector. The following are some exemplary specifications: Firewire power (8V-30V DC IN, 10 W Max). In one embodiment, Firewire may be designed to the IEEE 1394 A Spec (400 Mb/s).

USB Interface

The media player provides two configurations, or modes, of USB device operation: mass storage and media player USB Interface (MPUI). The MPUI allows the media player to be controlled using a media player accessory protocol (MPAP) which will be described in detail later herein, using a USB Human Interface Device (HID) interface as a transport mechanism.

Accessory 3.3 V Power

FIG. 4B illustrates the accessory power source. The media player accessory power pin supplies voltages, for example, 3.0 V to 3.3V+/−5% (2.85 V to 3.465 V) over the 30-pin docking connector and remote connector (if present). A maximum current is shared between the 30-pin docking and Audio/Remote connectors.

By default, the media player supplies a particular current such as 5 mA. Proper software accessory detection is required to turn on high power (for example, up to 100 mA) during active device usage. When devices are inactive, they must consume less than a predetermined amount of power such as 5 mA current.

Accessory power is grounded through the Digital GND pins.

FIG. 4C illustrates a reference schematic diagram for a system for detecting and identifying accessories for the docking connector. The system comprises a resistor to ground that allows the device to determine what has been plugged into the docking connector. There is an internal pull-up on Accessory Identify within the media player. Two pins are required (Accessory Identify & Accessory Detect).

FIG. 4D is a reference schematic of an electret microphone that may be connected to the remote connector.

Serial Protocol Communication:

a) Two pins used to communicate to and from device (Rx & Tx)

b) Input & Output (OV=Low, 3.3V=High)

As mentioned previously, media players connect to a variety of accessories. FIGS. 5A-5E illustrate a media player 500 coupled to different accessories. FIG. 5A illustrates a media player 500 coupled to a docking station 502. FIG. 513 illustrates the media player 500′ coupled to a computer 504. FIG. 5C illustrates the media player 500″ coupled to a car or home stereo system 506. FIG. 5D illustrates the media player 500′″ coupled to a dongle 508 that communicates wirelessly with other devices. FIG. 5E illustrates the media player 500″″ coupled to a speaker system 510. As is seen, what is meant by accessories includes but is not limited to docking stations, chargers, car stereos, microphones, home stereos, computers, speakers, and accessories which communicate wirelessly with other accessories.

As mentioned previously, this connector interface system could be utilized with a command set for authenticating an accessory. In one embodiment, the accessory may be a host computer or any other electronic device or system that may communicate with the media player. It should be understood by one of ordinary skill in the art that although the above-identified connector interface system could be utilized with the command set, a variety of other connectors or systems could be utilized and they would be within the spirit and scope of the present invention.

As described above, accessories interact with the media player using a media player accessory protocol. An example of such a media player accessory protocol is the iPod Accessory Protocol (iAP). The media player accessory protocol refers to the software component executing on the media player that communicates with accessories over a given transport layer. The application of the media player may be, for example, a media player application framework that presents menus/screens to the user. Media player commands are associated with the processing of voice, video, and other data between the media player and the accessory. For example, commands may be associated with read operations and write operations to transfer and store information between the media player and the accessory. Accordingly, in one embodiment, for each command related to the media player, there is a reciprocal command for the accessory. In one embodiment, commands may be grouped and associated with specific accessory functionality.

Command Functionality

Although a plurality of commands is described herein below, one of ordinary skill in the art recognizes that many other commands could be utilized and their use would be within the spirit and scope of the present invention. Accordingly, the list of commands below is representative, but not exhaustive, of the types of commands that could be utilized to authenticate an accessory. Furthermore, it is also readily understood by one of ordinary skill in the art that a subset of these commands could be utilized by a media player or an accessory and that use would be within the spirit and scope of the present invention. A description of the functionality of some of these commands is described below.

Authentication of an Accessory

In previous authentication methods, the accessory transmits an identification message to the media player, where the identification message indicates that the accessory supports certain commands and supports authentication. The media player then transmits an acknowledgment message to the accessory. The media player then blocks access by the accessory until the entire authentication process completes. The media player may display a “Connecting . . . ” screen. The media player then confirms that the authentication version number that the accessory provides is the correct version number. If so, the media player transmits a challenge to be signed by the device. The media player then validates the authentication signature using a public key based on a device ID from the accessory. The following describes improvements over the previous authentication methods, in accordance with the present invention.

FIG. 6 is a flow chart, which illustrates a process for controlling access to a media player, in accordance with the present invention. As FIG. 6 illustrates, the process begins in step 602 where the media player performs a background authentication operation on the accessory, where the authentication certificate is validated. More specifically, during the background authentication operation, the accessory transmits authentication information to the media player, and the media player receives and then validates the certificate contained in the authentication information. In one embodiment, the authentication information may also include an authentication version number. Authentication certificates are described in more detail below. As described in more detail below, the media player does not wait until the entire authentication process completes but instead allows certain access before the authentication process completes. Next, in step 604, the media player performs a second authentication operation on the accessory, where an authentication signature is validated. More specifically, during the second authentication operation, the accessory transmits an authentication signature to the media player, and the media player receives and then validates the authentication signature. In one embodiment, the media player verifies the authentication signature using a public key. More detailed embodiments of the background authentication and second authentication operations are described below and shown in FIG. 7.

Although the authentication of an accessory is described herein, one of ordinary skill in the art recognizes that the procedures described herein may be applied to the authentication of the media player, and such applications would be within the spirit and scope of the present invention. For example, the same or similar steps described in FIG. 6 above and/or in FIG. 7 below may be utilized by an accessory to authenticate the media player.

Authentication Certificates

Standard authentication certificates function as containers for data such as the certificate creator (issuer, country, etc.), certificate type, valid certificate date ranges, and other metadata. Authentication certificates, also referred to as certificates or certs, are generated and signed by one or more certificate authorities (CAs) and have a unique serial number. In one embodiment, the certificate may be stored in an authentication coprocessor chip on the accessory. Authentication certificates in accordance with the present invention contain not only the metadata as in a standard authentication certificate but also device class information and a public key, which are described in more detail below.

As described in more detail below, the media player verifies certificates using a public key that is issued by the CA. The media player may also use the public key to verify a signed challenge. Certificates are used to transfer the public key and other accessory-specific information to the media player. Such accessory-specific information may contain, for example, device class information about the accessory. The device class determines what commands the accessory is permitted to use with respect to the media player. In one embodiment, the media player may add permissible commands to existing classes or add new device classes by means of a media player firmware update. New accessories may be supported by the media player when the CA issues new certificates to the accessory vendor.

In one embodiment, if a certificate is somehow compromised and cloned in counterfeit devices, the compromised serial number may be added to a certificate revocation list (or CRL) on the media player to prevent devices using the certificate from authenticating successfully. If the certificate parser of the media player does not recognize the cert's device class, the media player will reject the certificate. In one embodiment, a certificate to be used for device authentication may have a preset lifespan (e.g., in the range of 1-5 years, etc.), which may be set, for example, by a date. In one embodiment, certificate expiration could be accomplished by adding device serial numbers to the CRL after the expiration date has passed.

FIG. 7 is a flow chart, which illustrates a process for authenticating an accessory, in accordance with the present invention. As FIG. 7 illustrates, the process begins in step 702 where the media player and accessory exchange messages to determine whether the accessory supports certain commands and supports immediate authentication. More specifically, in one embodiment, the accessory transmits an identification message to the media player. The identification message includes a device identification (ID) and an indication that the accessory supports certain commands and supports authentication. In a preferred embodiment, support for immediate authentication is required. The media player then transmits an acknowledgment message to the accessory. In one embodiment, the media player notifies the application of the media player that the accessory is attempting to access the media player.

As described above, in one embodiment, the authentication operations are handled in the background to allow multiple cryptography options (e.g., RSA or SFEE) with/without hardware acceleration to be used. As a result, the media player is operative to process device commands after authentication has begun, before the authentication has completed, and through its successful completion. When device authentication fails (e.g., retry count and/or maximum time has been exhausted), the media player could lockout processing of incoming commands and prevent the device from interacting with media player. Media player applications will need to permit non-risky device use once authentication has started. Risky behavior is defined as anything that could permanently alter the media player behavior or download unsafe media. Examples of risky behavior to be avoided could be downloading executable media, or firmware updates. If authentication fails at some later point, the application of the media player could cancel any device-related activities and possibly report an error to the user (e.g., “Device is not supported”).

Referring still to FIG. 7, in step 704, during the background authentication operation, the media player transmits an authentication information request to the accessory. In one embodiment, the media player starts a timeout timer. Next, in step 706, the accessory transmits the authentication information to the media player. In one embodiment, the authentication information includes an authentication major version, an authentication minor version, and a public certificate, where the certificate may be divided up into sections if it is large (e.g., greater than 500 bytes). If the certificate is divided up into sections, upon receipt of the authentication information, the media player reassembles the certificate. When the certificate is fully assembled, the certificate is parsed for device class information. The media player then converts a class number from the device class information into an allowed command mask. This mask is used to validate that the commands identified by the device are allowed by the certificate. In other words, the media player validates the certificate based at least in part on the device class information.

Next, in step 708, the media player validates the authentication information. The authentication information may be invalid for a number of reasons. For example, the authentication information may be invalid if the authentication version is not valid, if the public certificate has expired or is on the certificate revocation list (CRL). If any of the authentication information is invalid, the background authentication operation fails. A failure will restart the authentication process (if a retry count and timeout limits have not been exceeded). The background authentication operation passes if the authentication version is validated and if the certificate class commands have been determined to match or exceed those requested by an identify command of the media player, and if a certification chain has been verified. In one embodiment, non-risky media player command application functions and command processing are enabled while authentication process continues. In one embodiment, the media player may transmit a message to the accessory indicating a version information status.

Next, in step 710, during a second authentication operation, the media player transmits an authentication signature request to the accessory. The authentication signature request includes a random nonce/challenge to be signed by the device. The specific nonce/challenge length may vary and will depend on the specific implementation. Next, in step 712, the accessory transmits an authentication signature (i.e., a message with a signed challenge/signature) to the media player. Next, in step 714, upon receipt of the authentication signature, the media player validates the authentication signature (i.e., the signed challenge). In one embodiment, the media player verifies the signed nonce/challenge using a public key based on a device ID from the accessory. In a preferred embodiment, the media player verifies the signed nonce/challenge using a public key from the certificate provided by the accessory.

In one embodiment, an accessory authentication process (AAP) is based on a public key/private key system where the accessory has a private key and the media player has the associated public key. The accessory authentication process is closely integrated with accessory protocol commands.

Before completing the authentication process, the media player transmits an authentication status message to the accessory indicating signature status and authentication process completion. The authentication passes if the media player verifies the authentication signature. Otherwise, the authentication process fails. If authentication passes, the application of the media player unblocks to allow user access to the device.

If the authentication process fails, the device port of the media player will lock out the accessory. Also, upon a failure, the media player de-authorizes the accessory to prevent the accessory from utilizing the media player resources. In one embodiment, the media player may also transmit an authentication status to the application of the media player. For example, if the authentication fails, the application of the media player may display a “Connection Failed” message.

In one embodiment, the authentication operations may utilize a retry count and maximum timeout. Accordingly, in one embodiment, the authentication can also fail if the retry counter or maximum timeout is exceeded. Locking out a port prevents an accessory from simulating a detach or re-identifying in order to reset the authentication retry/timeout counters. In one embodiment, incoming packets may be deleted if a device port authentication state is set to “lockout.” This will prevent any locked out device packets from being processed. In one embodiment, if the failure is due to an accessory identifying more commands than allowed by the certificate, the device lockout will not be activated at authentication failure and the accessory may be permitted to re-identify.

A method, system, and connector interface for authenticating an accessory has been disclosed. The method includes performing a first authentication operation on the accessory by the media player, where an authentication certificate is validated. The method also includes performing a second authentication operation on the accessory by the media player, where an authentication signature is validated. According to the system and method disclosed herein, the media player and accessory may utilize a plurality of commands in a variety of environments such as within a connector interface system environment to control access to the media player.

Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. For example, the present invention can be implemented using hardware, software, a computer readable medium containing program instructions, or a combination thereof. Software written according to the present invention is to be either stored in some form of computer-readable medium such as memory or CD-ROM, or is to be transmitted over a network, and is to be executed by a processor. Consequently, a computer-readable medium is intended to include a computer readable signal, which may be, for example, transmitted over a network. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. 

What is claimed is:
 1. A media player comprising: a processor; and an accessory interface coupled to the processor and configured to communicate with an accessory; wherein the processor: sends a request for an authentication certificate to the accessory; and receives an authentication certificate from the accessory; determines a validity of the authentication certificate; and if the authentication certificate is not valid, then preventing the accessory from further interacting with the media player; otherwise the processor then receives an application command from the accessory and sends a request for an authentication signature; in response to the received application command, invokes an associated media player application function; and receives an authentication signature from the accessory; then determines a validity of the authentication signature.
 2. The media player of claim 1 further comprising: if the authentication signature is not valid, then the processor ignores any subsequent application command received from the accessory, otherwise the processor invokes corresponding media player application functions in response to subsequent application commands received from the accessory.
 3. The media player of claim 2 wherein if the processor determines that the authentication signature is valid, the processor determines that the authentication operation completed successfully.
 4. The media player of claim 3 wherein the processor communicates with an accessory according to a media player accessory protocol that defines a plurality of application commands to invoke a plurality of media player application functions.
 5. The media player of claim 4 wherein the authentication certificate includes authentication major version information and an authentication minor version information.
 6. The media player of claim 4 wherein the processor determines the validity of the authentication signature by: extracting a public key from the authentication certificate; and use the public key to validate the authentication signature.
 7. A media player comprising: a processor; and an accessory interface coupled to the processor and configured to communicate with an accessory; wherein the processor: sends a request for an authentication certificate to the accessory; and receives an authentication certificate from the accessory; determines a validity of the authentication certificate; and if the authentication certificate is not valid, then preventing the accessory from interacting with the media player; otherwise the processor then receives an application command from the accessory and sends a request for an authentication signature; in response to the received application command, does not invoke an associated a media player application function if the received application command can either permanently alter the media player behavior or download unsafe media, and otherwise invokes the associated media player application function; and receives an authentication signature from the accessory; then determines a validity of the authentication signature.
 8. The media player of claim 7 further comprising: if the authentication signature is not valid, then the processor ignores any subsequent application command received from the accessory, otherwise the processor invokes corresponding media player application functions in response to subsequent application commands received from the accessory.
 9. The media player of claim 8 wherein if the processor determines that the authentication signature is valid, the processor determines that the authentication operation completed successfully.
 10. The media player of claim 9 wherein the processor communicates with an accessory according to a media player accessory protocol that defines a plurality of application commands to invoke a plurality of media player application functions.
 11. The media player of claim 10 wherein the authentication certificate includes authentication major version information and an authentication minor version information.
 12. The media player of claim 10 wherein the processor determines the validity of the authentication signature by: extracting a public key from the authentication certificate; and use the public key to validate the authentication signature.
 13. An accessory comprising: a controller; and a media player interface coupled to the controller to communicate with a media player, wherein the controller: receives a request for an authentication certificate from the media player, the request for an authentication certificate initiating an authentication operation; sends an authentication certificate to the media player in response to the request for an authentication certificate, wherein the media player determines the validity of the authentication certificate; then receives a request for an authentication signature and sends an application command to the media player, wherein if the media player determines that the authentication certificate is not valid, the media player prevents the accessory from further interacting with the media player, and otherwise the media player allows the accessory to invoke a corresponding media player application function; then transmits an authentication signature to the media player for validation.
 14. The accessory of claim 13 further comprising: if the media player determines that the authentication signature is not valid, then the media player ignores any subsequent application command received from the accessory, otherwise the media player invokes corresponding media player application functions in response to subsequent application commands received from the accessory.
 15. The accessory of claim 14 wherein if the media player determines that the authentication signature is valid, the media player determines that the authentication operation completed successfully.
 16. The accessory of claim 15 wherein the media player interface communicates with the accessory according to a media player accessory protocol that defines a plurality of application commands to invoke a plurality of media player application functions.
 17. The accessory of claim 16 wherein the authentication certificate includes authentication major version information and an authentication minor version information.
 18. The accessory of claim 16 wherein the accessory provides the authentication signature by: receiving a challenge as part of the request for an authentication signature; and signing the received challenge.
 19. An accessory comprising: a controller; and a media player interface coupled to the controller to communicate with a media player, wherein the controller: receives a request for an authentication certificate from the media player, the request for an authentication certificate initiating an authentication operation; sends an authentication certificate to the media player in response to the request for an authentication certificate, wherein the media player determines the validity of the authentication certificate; then receives a request for an authentication signature and sends an application command to the media player, wherein if the media player determines that the authentication certificate is not valid, the media player prevents the accessory from further interacting with the media player, and if the authentication certificate is valid, the media player does not process the application command if the application command can either permanently alter the media player behavior or download unsafe media, otherwise the media player processes the application command thereby allowing the accessory to invoke a corresponding media player application function; then transmits an authentication signature to the media player for validation.
 20. The accessory of claim 19 further comprising: if the media player determines that the authentication signature is not valid, then the media player ignores any subsequent application command received from the accessory, otherwise the media player invokes corresponding media player application functions in response to subsequent application commands received from the accessory.
 21. The accessory of claim 20 wherein if the media player determines that the authentication signature is valid, the media player determines that the authentication operation completed successfully.
 22. The accessory of claim 21 wherein the media player interface communicates with the accessory according to a media player accessory protocol that defines a plurality of application commands to invoke a plurality of media player application functions.
 23. The accessory of claim 22 wherein the authentication certificate includes authentication major version information and an authentication minor version information.
 24. The accessory of claim 22 wherein the accessory provides the authentication signature by: receiving a challenge as part of the request for an authentication signature; and signing the received challenge. 